The present invention relates to a glass fiber optic unit and to a process for the production thereof.
Fiber optic units consist of one or several light waveguides bonded to one another and/or to a sleeve at their ends. Light waveguides are customarily glass fibers exhibiting a higher index of refraction in their interior than in their external glass region. Fiber optic units are utilized in many areas of technology as probes or lightguides for the transmission of optical measuring signals, for example in the fields of pyrometry, measuring signal processing in high-temperature chambers, or light transmission of a light of high power density from high-power light sources.
German Patent 3,744,367 concerns the production of fiber optic units, especially fiber optic conductor bundles. The production of a fiber optic unit which is heat-resistant up to about 350.degree. C. is accomplished by means of a press die, a glass ring, and a sleeve which are arranged over a region of a lightguide fiber bundle, after heating the fiber bundle substantially in the zone of the glass ring, then press-bonding same and allow it to cool, using a sleeve material which is not wetted by the heated glass of the ring. After cooling, at least the sleeve and optionally the die are again removed from the lightguide, in contrast to German Patent 3,247,500 which likewise describes a method for the manufacture of lightguides that are heat-resistant up to about 300.degree. C. but wherein the sleeve and die must remain on the prepared lightguide end, which is a disadvantage.
DOS 3,822,885 concerns optical fiber bundles for endoscopes or the like with a plurality of optical fibers joined on both ends but wherein individual fibers are freely movable within the central section of the bundle, which is encompassed by a flexible tube, for example of polyurethane. In order to avoid breakage of fibers, the flexible tube is filled, in the proximity of the ends, for example with liquid silicone, powdered molybdenum sulfide, or boron nitride. The fiber end zones, however, are connected at each end with a conventional metallic cap which disadvantageously also remains on the finished fiber bundle.
In order to couple in a high power density light into the ground and polished ends of the fiber optic unit, it is necessary for the connection of the glass fibers with one another and/or with the sleeve to be high-temperature refractory (T &gt;350.degree. C.) since, on the one hand, not all light can be coupled into the light waveguides so that a portion of the light also impinges on the junction points between the glass fibers and/or between the glass fiber(s) and the sleeve, thus heating this junction and, on the other hand, the field of usage of the fiber optic unit may make such a high-temperature resistance necessary.
Besides a sleeve, an adhesive is customarily if used in the preparation of fiber optic units. However, the organic adhesives, e.g., epoxy resins or polyimides, heretofore usually employed for joining glass fibers are temperature-resistant at most only to 280.degree. C. Consequently, organic adhesives are damaged when the fiber optic unit is used with a light of high power density. During such use, the adhesive evaporates and can precipitate on the end face of the glass fibers in the form of an interfering film, or it can burn up directly. Either result leads to uselessness and destruction of the entire fiber optic unit. Furthermore, the organic adhesives do not reflect light and, as a result, the heat stress on the adhesive is still further increased.
When using cements as bonding agents for the aforementioned purpose, a strong heating effect is likewise encountered for the additional reason that the light is not reflected by the bonding agent. Also, since these cements cannot be adapted with respect to their thermal expansion properties to the glass fibers, stresses can occur upon heating of the fiber optic unit that can lead to destruction of the fiber optic unit just as can happen by a temperature gradient developing due to differing heating up rates of the individual components.
The primary drawback in using a water glass composition as a bonding agent is the lack of resistance of the bond produced therefrom to the effect of moisture. There is a danger of redissolution of the water glass composition upon contact of the fiber optic unit with water and, as a consequence, the possible destruction of the fiber optic unit, for example when using the fiber optic unit in medical technology (cleaning, sterilization, etc.).
It is an object of the present invention to provide fiber optic units of the type discussed hereinabove which can be used under high power densities loads.
It is another object to provide a simple and inexpensive manufacturing method for producing such fiber optic units.
Other objects will be apparent to those skilled in the art to which this invention pertains.